The candidate's long-term goals include: (1) the continued study of age-related changes in autonomic control of the circulation during acute physical stress, and of the efficacy of regularly performed exercise in attenuating age-associated deterioration in cardiovascular function; (2) consistent publication of findings in highly respected scientific journals; (3) providing rigorous pre- and postdoctoral research training planning in cardiovascular aging research. The purpose of the present study will be to determine: (a) if regularly performed, endurance exercise significantly lowers blood pressure in men and women between 60-75 years of age with mild hypertension (blood pressure = 140-170 and/or 90-100); (b) if blood pressure can be reduced with exercise of mild intensity or if more strenuous exercise is necessary; and (c) the mechanisms which mediate training-induced reductions in blood pressure in older hypertensive subjects. To answer these questions, 66 older hypertensive subjects will perform mild (N=23) or strenuous (N=23) exercise or serve as non-exercising controls (N=20) for one year or longer. Blood pressure at rest and over the course of an entire day (24-hr ambulatory recordings) will be determined before and at 6-month intervals during training. Cardiac output, systemic vascular resistance, heart rate, stroke volume, cardiac autonomic efferent activity, cardiac dimensions and contractility, efferent sympathetic nerve activity (SNA), and carotid and cardiopulmonary baroreceptor regulation of heart rate and efferent SNA will be either measured or calculated at the same time points to determine the mechanisms by which blood pressure is reduced. The hypothesis is that regular exercise will reduce blood pressure primarily through a reduction in vascular resistance mediated by a decrease in efferent SNA.